This reaction is called dehydration of alcohol and the products usually formed are alkene and water. The products will be CH3CH=CH3 +H2O .

To understand this you have to understand the Saytzeff rule - hydrogen is eliminated from that carbon atom which has less number of hydrogen atoms attached to it. Thus the above reaction proceeds as given.

Mechanism - 1. Attachment of proton to alcoholic oxygen

2. Removal of H2O molecule

3. Removal of proton

As Al2O3 is a strong oxidising agent the reaction mechanism goes in same way as with H2SO4 / Heat.